1. Field of the Invention
The present invention relates to an apparatus for performing energy transfer among a plurality of battery devices interconnected in series and carried on an electric car or a hybrid car and thereby equalizing each voltage across each of the plurality of battery devices interconnected in series.
2. Description of the Related Art
The related art in this field is disclosed, for example, in Japanese Laid-Open Patent Publication No. Hei 11-176483 and U.S. Pat. No. 5,003,244. In the configuration of the former patent as shown in FIG. 7, the output voltages E1 to En of a plurality of battery devices 1-1 to 1-n are interconnected in series. For the purpose of the balance correction of the output voltages of the plurality of battery devices, a switching transistor 2 connected to a primary coil Np in series is switched ON and OFF in response to the output voltages. A converter is composed of a plurality of secondary coils Ns each corresponding to each of the plurality of battery devices and wound on a common transformer core with the primary coil. The connection thereof is configured such that the secondary output of the converter charges each battery device. When the switching transistor 2 is periodically switched ON and OFF, a voltage depending on the turn number ratio is generated in each secondary coil Ns. Since the plurality of secondary coils are wound on the common core, the induced charging current concentrates in a battery device having the lowest voltage among the plurality of battery devices, whereby the plurality of battery devices are equalized in voltage.
In this former circuit, in addition to that the switching transistor is simply switched ON and OFF, the current Ip flowing in the primary coil Np is controlled depending on the load current Io.
Further, in the configuration of the latter patent as shown in FIG. 8, the output voltages of a plurality of battery devices 25, 26, 27, 28 are connected in series. For the purpose of the balance correction of the output voltages of the plurality of battery devices, a switching transistor 34 connected to a primary coil 16 in series is switched ON and OFF in response to the input from a power supply 30. A converter 14 is composed of a plurality of secondary coils 21, 22, 23, 24 each corresponding to each of the plurality of battery devices and wound on a common transformer core with the primary coil 16. The connection thereof is configured such that the secondary output of the converter 14 charges each battery device. When the switching transistor 34 is periodically switched ON and OFF, a voltage depending on the turn number ratio is generated in each secondary coil. Since the plurality of secondary coils are wound on the common core, the induced charging current concentrates in a battery device having the lowest voltage among the plurality of battery devices, whereby the plurality of battery devices are equalized in voltage.
There has been the following problems in such above-mentioned related art apparatuses for equalizing the voltages across each of a plurality of energy storage means (battery devices) interconnected in series by means of the switching of a converter.
(a) In each above-mentioned related art apparatus, the magnetizing force is one directional in the transformer core for the ON and OFF duration of the switching device (transistor). Accordingly, the range of the change in magnetic flux density of the core is small, and hence the utilization of the core is less efficient. The lower efficiency in core utilization implies the necessity of a larger cross section in the core for a specific output power, thereby causing the problems of a larger apparatus and a higher cost.
Further, the switching ON and OFF of the switching device for the voltage equalizing causes a problem that electric charge stored in the capacitance existing between the terminals of the switching device for the OFF duration of the switching device is discharged by the next ON operation thereby to cause a power loss and a noise due to the short-circuit current.
(b) In each above-mentioned related art apparatus, energy stored in the transformer for the ON duration of the switching device is discharged for the next OFF duration of the switching device, thereby charging a battery device having the lowest voltage among the plurality of battery devices thereby to equalize the output voltages of the plurality of battery devices. Accordingly, the amount of equalizing energy is only the amount of energy stored for the ON duration of the switching device. Therefore, in order to increase the equalizing action, a larger switching device is necessary for increasing the equalizing current. However, this larger switching device causes a larger apparatus and hence a higher cost, as is the above-mentioned case (a). Further, since each battery device has an internal resistance, the higher current from the switching device causes a larger voltage drop across the internal resistance, thereby increasing apparent output voltage of the battery device in charging. This causes a problem of reducing the precision of output voltage equalizing.
An object of the present invention is to resolve the above-mentioned disadvantages (a) and (b) thereby to provide a voltage equalizing apparatus having a high efficiency and a high precision of equalizing and being of a small size.
In order to resolve the above-mentioned problems, in a voltage equalizing apparatus for battery devices, wherein each of a plurality of closed circuits is constituted of each of a plurality of battery devices (1-1 to 1-n) interconnected in series on a secondary side, each of a plurality of secondary windings (4-1 to 4-n) magnetically coupled with each other in a transformer (3), and each of a plurality of switching devices (2-1 to 2-n) on the secondary side, wherein a closed circuit is constituted of a battery device (1-m) on a primary side, a primary winding (4-m) magnetically coupled with the secondary windings in common, and a switching device (2-m) on the primary side, and wherein the plurality of switching devices on the secondary side and the switching device on the primary side are alternately switched ON and OFF, thereby equalizing the output voltages of the plurality of battery devices (1-1 to 1-n) interconnected in series on the secondary side; the ON operation of the plurality of switching devices (2-1 to 2-n) on the secondary side is continued until after the completion of release of exciting energy stored in the transformer by an ON operation of the switching device (2-m) on the primary side, into the plurality of battery devices on the secondary side through the plurality of switching devices (2-1 to 2-n) on the secondary side, whereby the above-mentioned object is achieved.
Further, means for detecting the variation in the output voltages of the plurality of battery devices (1-1 to 1-n) interconnected in series on the secondary side is provided, whereby in case of a large variation, the ON duration of the switching device (2-m) on the primary side and/or the plurality of switching devices (2-1 to 2-n) on the secondary side is extended.
In case of a small variation in the output voltages of the plurality of battery devices interconnected in series on the secondary side, the ON/OFF operation of the switching devices on the first and primary sides is stopped, and/or the ON duration of the switching devices on the first and primary sides is extremely shortened. This avoids power loss and noise due to unnecessary voltage equalizing operation in case of the small variation in the output voltages.
In case that the variation in the output voltages of the plurality of battery devices interconnected in series on the secondary side becomes smaller than a predetermined value, the ON duration of the switching device on the first and/or of the switching devices on the primary sides is shortened for reducing a equalizing current flowing among the first battery devices, whereby the precision increases in equalizing the terminal voltages of the battery devices.
In case that a current greater than or equal to a predetermined value flows through the plurality of battery devices interconnected in series on the secondary side, the ON/OFF operation of the switching devices on the first and primary sides is stopped, and/or the ON duration of the switching devices on the first and primary sides is extremely shortened, whereby the voltage equalizing operation is substantially stopped when the cell voltage detection of each battery device is affected by a voltage drop generated across the internal resistance of the battery device by a high current flowing through the plurality of battery devices interconnected in series on the secondary side.
During the charge from an external power supply and the discharge to an external load by the plurality of battery devices interconnected in series on the secondary side, the ON/OFF operation of the switching devices on the first and primary sides is stopped, and/or the ON duration of the switching devices on the first and primary sides is extremely shortened, whereby the voltage equalizing operation is stopped, even without current detection, automatically in response to the operation of a switch (S11) for switching the charge and discharge modes.
When the plurality of switching devices on the secondary side and the switching device on the primary side are alternately switched ON and OFF, there is a pause in an interval from the switching-OFF of the plurality of switching devices on the secondary side to the switching-ON of the switching device on the primary side and in an interval from the switching-OFF of the switching device on the primary side to the switching-ON of the plurality of switching devices on the secondary side, whereby each switch can be switched ON under the condition of substantially no electric charge in the capacitance component between the terminals of the switch in question (zero-volt switching).
A plurality of modules, wherein in each of the plurality of modules, each of a plurality of closed circuits is constituted of each of a plurality of battery devices interconnected in series on a secondary side, each of a plurality of secondary windings magnetically coupled with each other, and each of a plurality of switching devices on the secondary side, and wherein each of the plurality of modules comprises a transformer having at least a module equalizing winding magnetically coupled with the plurality of secondary windings in common, are provided; and the module equalizing windings each provided in each of the plurality of modules are interconnected in parallel; at least one of the plurality of modules is provided with an exciting winding magnetically coupled with the plurality of secondary windings involved in the module in question; a closed circuit is constituted by the serial connection of the exciting winding, a battery device on a primary side, and a switching device on the primary side; the ON operation of the plurality of switching devices on the secondary side is continued until after the completion of release of exciting energy stored in the transformer by an ON operation of the switching device on the primary side, into the plurality of battery devices on the secondary side through the plurality of switching devices on the secondary side; where by voltage equalizing operation similar to that within each single module is achieved also among the plurality of modules, whereby overall voltage equalizing operation is obtained.
Accordingly, there is a further effect that a necessary output voltage can be obtained by an appropriate combination of single modules.
The combination use of the exciting winding and the module equalizing winding permits a miniaturization of the apparatus.
In a voltage equalizing method for battery devices, wherein each of a plurality of closed circuits is constituted of each of a plurality of battery devices (1-1 to 1-n) interconnected in series on a secondary side, each of a plurality of secondary windings (4-1 to 4-n) magnetically coupled with each other in a transformer (3), and each of a plurality of switching devices (2-1 to 2-n) on the secondary side, wherein a closed circuit is constituted of a battery device (1-m) on a primary side, a primary winding (4-m) magnetically coupled with the secondary windings in common, and a switching device (2-m) on the primary side, and wherein the plurality of switching devices on the secondary side and the switching device on the primary side are alternately switched ON and OFF, thereby equalizing the output voltages of the plurality of battery devices interconnected in series on the secondary side; the ON operation of the plurality of switching devices (2-1 to 2-n) on the secondary side is continued until after the completion of release of exciting energy stored in the transformer by an ON operation of the switching device (2-m) on the primary side, into the plurality of battery devices on the secondary side through the plurality of switching devices (2-1 to 2-n) on the secondary side, whereby the above-mentioned object is achieved.
The ON duration of the switching device (2-m) on the primary side is controlled depending on the variation in the output voltages of the plurality of battery devices interconnected in series on the secondary side, whereby the voltage equalizing is performed more effectively depending on the value of the variation.
Means for detecting the variation in the output voltages of the plurality of battery devices (1-1 to 1-n) interconnected in series on the secondary side is provided, whereby in case of a large variation, the ON duration of the switching device (2-m) on the primary side and/or the plurality of switching devices (2-1 to 2-n) on the secondary side is extended.
In case that the variation in the output voltages of the plurality of battery devices interconnected in series on the secondary side becomes smaller than a predetermined value, the ON duration of the switching device on the first and/or of the switching devices on the primary sides is shortened for the reduction of power consumption for the equalizing, whereby the precision increases in equalizing the terminal voltages of the battery devices.
In case of a small variation in the output voltages of the plurality of battery devices interconnected in series on the secondary side, the ON/OFF operation of the switching devices on the first and primary sides is stopped, and/or the ON duration of the switching devices on the first and primary sides is extremely shortened. This avoids power loss and noise due to unnecessary voltage equalizing operation in case of the small variation in the output voltages.
In case that a current greater than or equal to a predetermined value flows through the plurality of battery devices interconnected in series on the secondary side, the ON/OFF operation of the switching devices on the first and primary sides is stopped, and/or the ON duration of the switching devices on the first and primary sides is extremely shortened, whereby the voltage equalizing operation is substantially stopped when the cell voltage detection of each battery device is affected by a voltage drop generated across the internal resistance of the battery device by a high current flowing through the plurality of battery devices interconnected in series on the secondary side.
During the charge from an external power supply and the discharge to an external load by the plurality of battery devices interconnected in series on the secondary side, the ON/OFF operation of the switching devices on the first and primary sides is stopped, and/or the ON duration of the switching devices on the first and primary sides is extremely shortened, whereby the voltage equalizing operation is stopped, even without current detection, automatically in response to the operation of a switch (S11) for switching the charge and discharge modes.
When the plurality of switching devices on the secondary side and the switching device on the primary side are alternately switched ON and OFF, there is a pause in an interval from the switching-OFF of the plurality of switching devices on the secondary side to the switching-ON of the switching device on the primary side and in an interval from the switching-OFF of the switching device on the primary side to the switching-ON of the plurality of switching devices on the secondary side, whereby each switch can be switched ON under the condition of substantially no electric charge in the capacitance component between the terminals of the switch in question (zero-volt switching).